Vehicle gear-shifting control apparatus

ABSTRACT

A vehicle gear-shifting control apparatus is equipped with an engine, a motor, an automatic transmission, a friction brake system, and a controller which executes a regeneration control of imparting a regenerative braking torque to rear wheels by causing the motor to perform a regeneration operation and a gear-shifting control of changing a shift stage of the automatic transmission by outputting a gear-shifting signal in accordance with the rotation speed of an input shaft. The controller starts the gear-shifting control, triggered by the rotation speed decreasing to a predetermined downshift point during a downshift of the shift stage, and during deceleration of the vehicle when a coefficient of friction of a road surface is lower than a predetermined threshold in the regeneration control, the controller sets the downshift point lower than when the coefficient of friction is equal to or higher than the threshold.

TECHNICAL FIELD

The technique disclosed herein relates to a vehicle gear-shiftingcontrol apparatus.

BACKGROUND ART

For example, JP2016-132432A describes a control apparatus of a hybridvehicle. The hybrid vehicle is equipped with an engine, a motor, and anautomatic transmission. The engine and the motor are connected to aninput shaft of the automatic transmission. The hybrid vehicle improvesfuel efficiency performance by having the motor perform a regenerationoperation when the automatic transmission performs a downshift.

In particular, the automatic transmission described in JP2016-132432Ahas a plurality of friction control mechanisms which independentlycontrol each of a plurality of friction elements. When indicatingindicated hydraulic pressures to first and second friction controlmechanisms among the plurality of friction control mechanisms, thecontrol apparatus applies a delay operation processing to the indicatedhydraulic pressures. According to JP2016-132432A, by applying the delayoperation processing to each indicated hydraulic pressure, a temporalresponse delay can be taken into consideration.

SUMMARY OF INVENTION Problem to be Solved by the Invention

With a rear-wheel drive vehicle in which an output shaft of an automatictransmission is connected to rear wheels, when a motor performs aregeneration operation, a regenerative braking torque is only impartedto the rear wheels. Therefore, for example, when the motor performs theregeneration operation during deceleration, the rear wheels are apt tofall into a slip state. When the slip state deteriorates, for example,the rear wheels skid when turning while decelerating and a behavior ofthe vehicle is liable to fall into a so-called oversteered state.

When the vehicle enters the oversteered state, the regenerationoperation of the motor can conceivably be stopped. In other words, sincestopping the regeneration operation of the motor causes a braking forcecorresponding to a regenerative braking torque thereof to be distributedto the front wheels and the rear wheels by friction brakes, the slipstate of the rear wheels and, eventually, the oversteered state of thevehicle are resolved. However, stopping the regeneration operationcauses fuel efficiency performance of the hybrid vehicle to decrease andis, therefore, inconvenient.

Unfortunately, with conventional hybrid vehicles, the regenerationoperation under circumstances where the oversteered state is a concernin a rear-wheel drive vehicle such as when rear wheels fall into theslip state has not been sufficiently studied and it was impossible toachieve both suppression of oversteering and securement of aregeneration amount at the same time.

The technique disclosed herein has been devised in view of this pointand an object thereof is to achieve both securement of as much of aregeneration amount as possible and an improvement in robustness in arear-wheel drive vehicle.

Means for Solving the Problem

The present inventors analyzed a relationship among a gear-shiftingcontrol, a regeneration operation of a motor, and oversteering duringdeceleration of a vehicle. According to the analysis, it was found thatan oversteered state is likely to occur when gear-shifting by anautomatic transmission and the regeneration operation by the motor areperformed in parallel.

However, susceptibility to the oversteered state is also influenced by acoefficient of friction (μ) of a road surface. Specifically, when thecoefficient of friction is high, since skidding of the rear wheels issuppressed, the oversteered state is less likely to occur than when thecoefficient of friction is low. In this case, even if the gear-shiftingcontrol and the regeneration operation are performed in parallel, anoccurrence of the oversteered state is conceivably suppressed.

Therefore, when the coefficient of friction is high, conceivably,adopting a configuration of setting a high downshift point (a thresholdof the input rotation speed of the automatic transmission) whichtriggers a downshift during deceleration and starting the downshift atan earlier timing and at a higher rotation speed does not pose aninconvenience. Since the regeneration operation on a high-rotation-speedside enables a regeneration amount to be increased as compared to alow-rotation-speed side, a contribution is made toward improving fuelefficiency performance.

In contrast, when the coefficient of friction is low, the oversteeredstate is more likely to occur than when the coefficient of friction ishigh. In this case, while the gear-shifting control and the regenerationoperation may conceivably be scheduled not to be performed in parallel,prohibiting the gear-shifting control causes discomfort and is thereforeinconvenient.

On the other hand, according to an analysis by the present inventors,since a regeneration amount decreases as the input rotation speed of theautomatic transmission decreases once a certain period elapses fromstart of deceleration of a vehicle, the vehicle recovers from a slipstate and an occurrence of the oversteered state is suppressed, or evenif the oversteered state has already occurred, the oversteered state isresolved. However, it was newly found that, since the timing of recoveryfrom the slip state in this case arrives after a start timing ofgear-shifting, the oversteered state is likely to occur as a result ofthe gear-shifting being performed before a recovery from the slip stateis made.

In consideration thereof, adoption of a configuration was newlyconceived in which, due to delaying the start timing of gear-shifting bysetting the downshift point lower during deceleration of the vehiclewhen the coefficient of friction is low than when the coefficient offriction is high, the gear-shifting control is started at a timing afterthe oversteered state is avoided or at a timing after the oversteeredstate is resolved and, consequently, the present disclosure was devised.

Specifically, the present disclosure relates to a vehicle gear-shiftingcontrol apparatus. The gear-shifting control apparatus includes anengine which is mounted to a vehicle and which generates a travel driveforce of the vehicle, a motor which generates another travel drive forceof the vehicle and which supplies a battery with regenerative energyduring deceleration of the vehicle, a hydraulically controlled automatictransmission which has an input shaft connected to the engine and themotor and an output shaft connected to rear wheels of the vehicle andwhich subjects an input rotation to gear-shifting at a transmission gearratio corresponding to a selected shift stage and outputs thegear-shifted input rotation, and a controller which executes, at leastduring deceleration of the vehicle, a regeneration control of impartinga regenerative braking torque to the rear wheels by causing the motor toperform a regeneration operation and a gear-shifting control of changingthe shift stage by outputting a gear-shifting signal in accordance withthe rotation speed of the input shaft to the automatic transmission. Thecontroller starts the gear-shifting control, triggered by the rotationspeed of the input shaft decreasing to a predetermined downshift pointduring a downshift of the shift stage.

In addition, according to the present disclosure, during deceleration ofthe vehicle when it is determined that a coefficient of friction of aroad surface on which the vehicle travels is lower than a predeterminedthreshold in the regeneration control, the controller sets the downshiftpoint lower than during deceleration of the vehicle when it isdetermined that the coefficient of friction is equal to or higher thanthe threshold.

According to the configuration described above, the regeneration controlis executed by causing the motor to perform the regeneration operationat least during deceleration of the vehicle. Due to the regenerationcontrol, regenerative energy accumulated in the battery increases. Aregenerative braking torque produced by the motor is only imparted tothe rear wheels through the automatic transmission.

In addition, during deceleration of the vehicle, the controller outputsa gear-shifting signal according to the rotation speed of the inputshaft to the automatic transmission, triggered by the rotation speed ofthe input shaft decreasing to a predetermined downshift point. Theautomatic transmission receives the gear-shifting signal and changes theshift stage or, in other words, executes a downshift of changing theshift stage from a high-speed stage to a low-speed stage. Duringdeceleration of the vehicle, a shift stage corresponding to anoperational state of the engine is selected.

In addition, during deceleration of the vehicle when it is determinedthat the coefficient of friction is equal to or higher than thepredetermined threshold, the controller sets the downshift pointrelatively high. When the coefficient of friction is high, an occurrenceof the oversteered state is suppressed even when adopting aconfiguration in which a downshift starts on a high-rotation-speed side.Since a regeneration operation on a high-rotation-speed side enables aregeneration amount to be increased as compared to a low-rotation-speedside, a contribution is made toward improving fuel efficiencyperformance.

On the other hand, during deceleration of the vehicle when it isdetermined that the coefficient of friction is lower than thepredetermined threshold, the controller sets the downshift pointrelatively low so that the downshift is started at a later timing.Accordingly, the gear-shifting control can be started after theoversteered state is avoided, or even if the oversteered state hasoccurred, the gear-shifting control can be started after the oversteeredstate is resolved. As a result, the behavior of the vehicle can bestabilized and robustness of the vehicle can be improved.

As described above, the gear-shifting control apparatus according to thepresent disclosure is capable of achieving both securement of as much ofa regeneration amount as possible due to the regeneration operation on ahigh-rotation-speed side and an improvement in robustness due todelaying a start timing of gear-shifting control.

In addition, according to an aspect of the present disclosure, duringacceleration of the vehicle when it is determined that the coefficientof friction is lower than the threshold, the controller may limit anupshift which causes the shift stage to be changed to a predeterminedstage or higher.

According to the aspect described above, during acceleration of thevehicle when the coefficient of friction is relatively low, a limitationis to be imposed on a highest stage among the shift stages. Accordingly,when the vehicle makes a transition from acceleration to deceleration, afrequency of occurrences of a downshift can be reduced. As a result,opportunities where oversteering may occur can be reduced and thebehavior of the vehicle can be stabilized.

Furthermore, according to an aspect of the present disclosure, when thedownshift point is set low based on the coefficient of friction and,subsequently, the rotation speed of the input shaft decreases to thedownshift point, the controller may interrupt motive power transmissionbetween the input shaft and the output shaft.

According to the aspect described above, when the rotation speed of theinput shaft decreases to the downshift point set relatively low, thecontroller interrupts motive power transmission between the input shaftand the output shaft instead of starting gear-shifting. Interruptingmotive power transmission results in a decrease in a torque acting onthe rear wheels. Accordingly, destabilization of the behavior of thevehicle such as an occurrence of the oversteered state can be suppressedand, at the same time, an engine stall due to a further decrease in therotation speed of the engine can be avoided.

In addition, according to an aspect of the present disclosure, thegear-shifting control apparatus includes a hydraulically controlledfriction brake system which distributes a braking force to front wheelsand the rear wheels of the vehicle in order to realize braking inaccordance with a brake pedal operation (an operation of a brake pedal)by a driver. During the regeneration control in a case where thecoefficient of friction is determined to be higher than the threshold,the controller may set the downshift point higher in a state ofdeceleration of the vehicle during the brake pedal operation than thestate of deceleration of the vehicle during a non-brake pedal operation(a non-operation of the brake pedal) under the same condition of thecoefficient of friction.

According to the aspect described above, in the course of decelerationduring a brake pedal operation, the rotation speed of the motor duringthe regeneration operation can be maintained at a high level by settinga downshift point relatively high. Maintaining a high rotation speed ofthe motor increases a regeneration amount and, eventually, improves fuelefficiency performance of the vehicle.

On the other hand, in the course of deceleration during a non-brakepedal operation, a change to an acceleration request may occur when thedriver depresses the accelerator pedal. In this case, when the rotationspeed of the input shaft of the automatic transmission is maintained ata high level due to setting the downshift point relatively high, thereis a risk that a sufficient drive force cannot be secured during theacceleration request by the driver.

In consideration thereof, the controller sets the downshift point of theautomatic transmission relatively low during a non-brake pedaloperation. Accordingly, since the rotation speed of the input shaft ofthe automatic transmission becomes relatively lower, a sufficient driveforce can be secured during the acceleration request by the driver.

In addition, according to an aspect of the present application, when anunstable behavior of the vehicle diverges after interrupting motivepower transmission between the input shaft and the output shaft, thecontroller may cause the friction brake system to execute a control forstabilizing the behavior of the vehicle by imparting the braking forceto the front wheels or the rear wheels.

In this case, control for stabilizing the behavior of the vehicleincludes DSC (Dynamic Stability Control) and ABS (Anti-lock BrakeSystem).

According to the aspect described above, when an unstable behavior ofthe vehicle diverges even after interrupting motive power transmissionbetween the input shaft and the output shaft, due to operation of DSC orABS, the behavior of the vehicle can be prevented from becominguncontrollable.

Furthermore, according to an aspect of the present disclosure, thecontroller may determine an oversteered state of the vehicle byreceiving signals of a first sensor which outputs a signal related to abehavior of the vehicle and a second sensor which outputs a signalrelated to a steering operation by the driver, and the controller maydetermine that the vehicle is engaging in an unstable behavior when thevehicle is in the oversteered state.

According to the aspect described above, the controller determines theoversteered state based on signals of the first sensor and the secondsensor. Accordingly, the controller can determine the behavior of thevehicle in a speedy and accurate manner.

Advantageous Effect of Invention

As described above, according to the present disclosure, both securementof as much of a regeneration amount as possible and an improvement inrobustness in a rear-wheel drive vehicle can be achieved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a hybrid automobile.

FIG. 2 shows a fastening table of an automatic transmission.

FIG. 3A is a block diagram of a gear-shifting control apparatus.

FIG. 3B is a block diagram explaining a base map of a gear-shiftingpoint.

FIG. 4 is a flow chart of overall control related to behavioralstability.

FIG. 5 is a diagram explaining a function of control related tobehavioral stability.

FIG. 6 is a flow chart of first processing.

FIG. 7 shows a downshift point for each shift stage of the automatictransmission.

FIG. 8 is a flow chart of second processing.

FIG. 9 is a flow chart of gear-shifting control.

FIG. 10 is a flow chart of third processing.

FIG. 11 is a flow chart of fourth processing.

FIG. 12 is a time chart of a case where a downshift is delayed.

FIG. 13 is a time chart of a case where, as a result of delaying adownshift, a K1 clutch of the automatic transmission is opened.

FIG. 14 is a time chart of a case where oversteering is determinedduring a downshift.

FIG. 15 is a flow chart related to a modification of the secondprocessing.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of a vehicle gear-shifting control apparatuswill be described with reference to the drawings. The gear-shiftingcontrol apparatus described herein is illustrative.

(Hybrid Automobile)

FIG. 1 shows an automobile 1 (an example of the vehicle) to which thedisclosed technique is applied. The automobile 1 is a hybrid automobilecapable of traveling using electric power. The automobile 1 has a totalof four wheels including front wheels 2F and rear wheels 2R. Frictionbrakes 31 are respectively attached to the front wheels 2F and the rearwheels 2R in order to apply braking on rotations of the front wheels 2Fand the rear wheels 2R.

An engine 4 and a motor 5 which generate a travel drive force of theautomobile 1 are mounted to the automobile 1 as drive sources. Theengine 4 and the motor 5 cooperate with each other to drive the rearwheels 2R. Accordingly, the automobile 1 travels. The automobile 1 is arear-wheel drive vehicle. The motor 5 is not only used as a drive sourcebut is also used as a generator during regeneration.

The automobile 1 is equipped with a high-voltage battery 9 of which arated voltage is 50 V or lower as will be described later. Due to supplyof electric power from the high-voltage battery 9, traveling is carriedout as the motor 5 mainly provides assistance to the engine 4 (aso-called mild hybrid vehicle). Alternatively, the automobile 1 may be aso-called plug-in hybrid vehicle to which electric power can be suppliedfrom an outside power source.

In the case of the automobile 1, the engine 4 is disposed on a frontside of a vehicle body and the drive wheels are arranged on a rear sideof the vehicle body. In other words, the automobile 1 is a so-calledfront-engine, rear-wheel drive (FR) vehicle.

In addition to the engine 4 and the motor 5, the automobile 1 isequipped with a K0 clutch 6, an inverter 7, and an automatictransmission 8 as apparatuses of a drive system. The automobile 1 isalso equipped with a controller 20 as an apparatus of a control system.The automobile 1 is also equipped with a friction brake system 3including the friction brakes 31 as an apparatus of a brake system.

(Apparatuses of Drive System)

For example, the engine 4 is an internal combustion engine which burnsfossil fuel. The engine 4 is also a so-called four-cycle engine whichgenerates rotative power by repeating the respective cycles of intake,compression, expansion, and exhaust. While the engine 4 is available invarious types or modes such as a spark-ignited engine and acompression-ignited engine, the type or the mode of the engine 4 is notparticularly limited in the disclosed technique.

In the automobile 1, the engine 4 is disposed approximately in a centerpart in a vehicle width direction in a state where a crankshaft 4 awhich outputs rotative power is oriented in a front-rear direction ofthe vehicle body. Various apparatuses and mechanisms associated with theengine 4 such as an intake system, an exhaust system, and a fuel supplysystem are installed in the automobile 1.

The motor 5 is a permanent magnet-type synchronous motor which is drivenby a three-phase AC current. The motor 5 is serially disposed to therear of the engine 4 via the K0 clutch 6. The motor 5 is also seriallydisposed to the front of the automatic transmission 8.

The K0 clutch 6 is installed so as to be interposed between a front endpart of a shaft 5 a of the motor 5 and the crankshaft 4 a of the engine4. The K0 clutch 6 switches between a state (connected state) in whichthe crankshaft 4 a and the shaft 5 a are connected to each other and astate (disconnected state) in which the crankshaft 4 a and the shaft 5 aare disconnected from each other.

A rear end part of the shaft 5 a of the motor 5 is connected to an inputshaft 8 a of the automatic transmission 8. Therefore, the engine 4 isconnected to the automatic transmission 8 via the K0 clutch 6 and theshaft 5 a. By putting the K0 clutch 6 in the disconnected state, theengine 4 is detached from the automatic transmission 8.

During traveling of the automobile 1, the K0 clutch 6 is switchedbetween the connected state and the disconnected state. For example,during deceleration of the automobile 1, regeneration may be performedin a state where the K0 clutch 6 is switched to the disconnected stateand the engine 4 is detached.

The motor 5 is connected via the inverter 7 and a high-voltage cable 40to the high-voltage battery 9 which is mounted as a drive power source.In the case of the automobile 1, a DC battery with a rated voltage of 50V or lower or, specifically, a 48 V DC battery is used as thehigh-voltage battery 9.

The high-voltage battery 9 supplies high-voltage DC electric power tothe inverter 7. The inverter 7 converts the DC electric power intothree-phase AC and feeds the converted power to the motor 5.Accordingly, the motor 5 is rotatively driven. In addition, the motor 5supplies regenerative energy to the high-voltage battery 9.

The high-voltage battery 9 is also connected to a DC-DC converter 10 viathe high-voltage cable 40. The DC-DC converter 10 converts high-voltageDC electric power of 48 V into low-voltage DC electric power of 12 V andoutputs the converted low-voltage DC electric power. The DC-DC converter10 (an output side thereof) is connected to a low-voltage battery 11 (aso-called lead-acid battery) via a low-voltage cable 41.

The low-voltage battery 11 is connected to various electrical componentsvia the low-voltage cable 41. The DC-DC converter 10 is also connectedto a CAN 12 (Controller Area Network) via the low-voltage cable 41.Accordingly, the DC-DC converter 10 supplies low-voltage DC electricpower to the CAN 12.

The automatic transmission 8 is a hydraulically controlled multi-stageautomatic transmission (a so-called AT). The automatic transmission 8has the input shaft 8 a to be connected to the engine 4 and an outputshaft 8 b to be connected to drive wheels (the rear wheels 2R) of theautomobile 1. The automatic transmission 8 is capable of gear-shifting arotation input to the input shaft 8 a by a transmission gear ratiocorresponding to a shift stage selected by an occupant and outputtingthe gear-shifted rotation.

Specifically, the input shaft 8 a is disposed in a front end part of theautomatic transmission 8. As described above, the input shaft 8 a isconnected to the shaft 5 a of the motor 5. The output shaft 8 b isdisposed in a rear end part of the automatic transmission 8. The outputshaft 8 b rotates independently of the input shaft 8 a.

A transmission mechanism made up of a torque converter 8 c, a pluralityof planetary gear mechanisms, a plurality of friction fasteningelements, and the like is built in between the input shaft 8 a and theoutput shaft 8 b. Each friction fastening element is switched between afastened state and a non-fastened state by hydraulic pressure.

FIG. 2 shows a fastening table of the automatic transmission 8. A circlesymbol in the table indicates fastening. Three clutches including afirst clutch CL1, a second clutch CL2, and a third clutch CL3 and twobrakes including a first brake BR1 and a second brake BR2 areincorporated into the automatic transmission 8 as friction fasteningelements.

The automatic transmission 8 selects and fastens three elements fromamong the three clutches and the two brakes according to hydrauliccontrol. Accordingly, the shift stage of the automatic transmission isswitched to any one of forward shift stages from a first speed to aneighth speed and a reverse shift stage (reverse speed).

Specifically, the first speed is formed by fastening of the first clutchCL1, the first brake BR1, and the second brake BR2. The second speed isformed by fastening of the second clutch CL2, the first brake BR1, andthe second brake BR2. The third speed is formed by fastening of thefirst clutch CL1, the second clutch CL2, and the second brake BR2. Thefourth speed is formed by fastening of the second clutch CL2, the thirdclutch CL3, and the second brake BR2. The fifth speed is formed byfastening of the first clutch CL1, the third clutch CL3, and the secondbrake BR2. The sixth speed is formed by fastening of the first clutchCL1, the second clutch CL2, and the third clutch CL3. The seventh speedis formed by fastening of the first clutch CL1, the third clutch CL3,and the first brake BR1. The eighth speed is formed by fastening of thesecond clutch CL2, the third clutch CL3, and the first brake BR1. Thereverse speed is formed by fastening of the third clutch CL3, the firstbrake BR1, and the second brake BR2.

In addition, for example, when shifting up from the first speed, byfastening the second clutch CL2 instead of the first clutch CL1, theshift stage is switched from the first speed to the second speed. Byfastening the first clutch CL1 instead of the first brake BR1, the shiftstage is switched from the second speed to the third speed. By fasteningthe third clutch CL3 instead of the first clutch CL1, the shift stage isswitched from the third speed to the fourth speed.

Shifting up to the fifth and higher speeds is performed in a similarmanner. Shifting down involves an opposite procedure to the switchingperformed when shifting up.

When elements to be fastened in each shift stage are not fastened, astate is created where the input shaft 8 a and the output shaft 8 b aredetached from each other (so-called neutral). Even when rotative poweris input to the automatic transmission 8 from the drive sources, therotative power is not output from the automatic transmission 8.

As will be described later, the automatic transmission 8 may be shiftedto neutral during deceleration of the automobile 1. Specifically, whenthe automatic transmission 8 is in the second speed, the third speed, orthe fourth speed, the automatic transmission 8 is shifted to neutral byopening the second clutch CL2. In addition, when the automatictransmission 8 is in the fifth speed, the sixth speed, the seventhspeed, or the eighth speed, the automatic transmission 8 is shifted toneutral by opening the third clutch CL3. In the following description,the second clutch CL2 and the third clutch CL3 may be collectivelyreferred to as a K1 clutch. Opening the K1 clutch during deceleration ofthe automobile 1 means interrupting motive power transmission betweenthe input shaft 8 a and the output shaft 8 b of the automatictransmission 8 and shifting the automatic transmission 8 to neutral.

As shown in FIG. 1 , the output shaft 8 b of the automatic transmission8 is connected to a differential gear 16 via a propeller shaft 15 whichextends in the front-rear direction of the vehicle body. A pair of driveshafts 17 which extend in a vehicle width direction and which isconnected to the left and right rear wheels 2R, 2R are connected to thedifferential gear 16. Rotative power output through the propeller shaft15 is distributed by the differential gear 16 and then transmitted toeach rear wheel 2R though the pair of drive shafts 17, 17.

(Gear-Shifting Control Apparatus)

FIG. 3A is a block diagram of a gear-shifting control apparatus. Thecontroller 20 described above is installed in the automobile 1 in orderto control the engine 4, the motor 5, the K0 clutch 6, the automatictransmission 8, the friction brake system 3, and the like according tooperations by the driver and to control traveling of the automobile 1.The controller 20 is made up of hardware including a processor, memory,and an interface and software including a database and a controlprogram. Note that while one controller 20 is shown in the gear-shiftingcontrol apparatus shown in FIG. 3A, the controller of the gear-shiftingcontrol apparatus may be divided into a unit (powertrain control module(PCM)) which mainly controls operations of the drive sources (the engine4 and the motor 5) and a unit (transmission control module (TCM)) whichmainly controls operations of the K0 clutch 6 and the automatictransmission 8. The PCM and the TCM are connected by the CAN 12 and areconfigured to be capable of performing telecommunications with eachother. The PCM further functions as a brake electronic control unit(ECU) for controlling the friction brake system 3. Alternatively, thebrake ECU may be separated from the PCM.

The gear-shifting control apparatus is equipped with sensors whichmeasure various parameters related to traveling of a vehicle.Specifically, the gear-shifting control apparatus is equipped with avehicle speed sensor 51, a wheel speed sensor 52, a steering anglesensor 53, a yaw rate sensor 54, a brake pedal sensor 55, an acceleratoropening sensor 56, an AT input torque sensor 57, and an AT inputrotation speed sensor 58.

The vehicle speed sensor 51 outputs a signal corresponding to a vehiclespeed of the automobile 1. The wheel speed sensor 52 outputs a signalcorresponding to the rotation speed of each wheel among the four wheels2F and 2R of the automobile 1.

The steering angle sensor 53 outputs a signal corresponding to arotation angle of a steering wheel 110 (refer to FIG. 1 ) operated bythe driver or, in other words, a steering angle. The yaw rate sensor 54outputs a signal corresponding to a yaw rate of the automobile 1.

The brake pedal sensor 55 outputs a signal corresponding to depressingof a brake pedal 19 (refer to FIG. 1 ) operated by the driver. Theaccelerator opening sensor 56 outputs a signal corresponding todepressing of an accelerator pedal 18 (refer to FIG. 1 ) operated by thedriver.

The AT input torque sensor 57 outputs a signal corresponding to an inputtorque of the input shaft 8 a of the automatic transmission 8. The ATinput rotation speed sensor 58 outputs a signal corresponding to therotation speed of the input shaft 8 a of the automatic transmission 8.

The controller 20 receives, via the CAN 12, signals output by thesensors. The controller 20 outputs control signals to the engine 4, theinverter 7, the K0 clutch 6, the automatic transmission 8, and thefriction brake system 3 through the CAN 12. Accordingly, the controller20 controls the engine 4, the motor 5, the K0 clutch 6, the automatictransmission 8, and the friction brake system 3.

For example, the controller 20 can execute a gear-shifting control ofchanging a shift stage of the automatic transmission 8. Thegear-shifting control involves changing the shift stage of the automatictransmission 8 by outputting a gear-shifting signal according to therotation speed of the input shaft 8 a to the automatic transmission 8.By changing the shift stage, an upshift and the downshift describedearlier can be realized. In doing so, the controller 20 executes thechange in the shift stage after adjusting a difference in rotation speedbetween the input shaft 8 a and the output shaft 8 b.

More specifically, the controller 20 starts the gear-shifting control(more accurately, the adjustment of a difference in rotation speedbetween the input shaft 8 a and the output shaft 8 b), triggered by thenumber of rotation speed of the input shaft 8 a decreasing to apredetermined downshift point during a downshift of the shift stage.Hereinafter, a downshift point may also be simply referred to as a“gear-shifting point.”

The controller 20 is also capable of controlling the friction brakesystem 3. The friction brake system 3 distributes a braking force to thefront wheels 2F and the rear wheels 2R of the automobile 1 so thatbraking is realized upon an operation of the brake pedal 19 by thedriver. The friction brake system 3 is a hydraulically controlledfriction brake system. A level of the hydraulic pressure corresponds toa level of the braking force distributed by the friction brakes 31.Specifically, when the hydraulic pressure is low, the braking force islow as compared to when the hydraulic pressure is high.

Furthermore, the controller 20 according to the present embodiment isalso capable of executing a regeneration control for performingregeneration of energy. The regeneration control involves performingregeneration according to at least one of distribution of a brakingforce by the friction brake system 3 and impartment of a regenerativebraking torque to the rear wheels 2R by the motor 5. In other words, thecontroller 20 is also capable of performing regeneration by coordinationbetween the distribution of a braking force and the impartment of aregenerative braking torque. Note that even cases where the frictionbrake system 3 is not involved in regeneration such as during anon-operation of the brake pedal 19 are also included in the“regeneration control” as referred to herein.

The controller 20 according to the present embodiment is capable ofexecuting the gear-shifting control and the regeneration control duringdeceleration of the automobile 1.

(Control Related to Behavioral Stability) <Entirety of Control>

FIG. 4 shows an entirety of control related to behavioral stability ofthe automobile 1. Note that the flows shown in FIG. 4 and FIGS. 6, 8 to11, and 15 to be described later are basically related to control duringdeceleration of the automobile 1.

During vehicle deceleration, the controller 20 executes a regenerativecoordination control or a second regeneration control as theregeneration control depending on whether or not the driver isdepressing the brake pedal 19. These types of regeneration correspond toso-called “decelerative regeneration.”

Specifically, during deceleration when the driver is depressing thebrake pedal 19, the controller 20 executes the regenerative coordinationcontrol in which a part of a required braking force of the driver iscovered by a regenerative braking torque of the motor 5. On the otherhand, during deceleration when the driver is not depressing the brakepedal 19, the controller 20 executes the second regeneration control inwhich regenerative braking corresponding to engine braking is performed.

FIG. 5 shows a concept of functions of control related to the behavioralstability of the automobile 1. The automobile 1 has three functions,namely, active control, passive control, and DSC/ABS (Dynamic StabilityControl/Anti-lock Brake System) control. Active control functions so asto keep a grip force of the wheels 2F and 2R within a circle of frictionillustrated in FIG. 5 . The behavioral stability of the automobile 1 ismaintained as long as the grip force of the wheels 2F and 2R stay withinthe circle of friction. Active control is control for maintaining thebehavioral stability of the automobile 1.

Passive control functions to return the grip force of the wheels 2F and2R into the circle of friction when the grip force of the wheels 2F and2R exceeds the circle of friction and the behavior of the automobile 1becomes unstable.

DSC/ABS control functions to return the grip force of the wheels 2F and2R into the circle of friction when the behavior of the automobile 1 isabout to diverge or, in other words, when the grip force of the wheels2F and 2R is about to exceed a circle with a largest diameter by havingthe friction brake system 3 impart a braking force to each of the wheels2F and 2R through the friction brakes 31. Known techniques can beadopted for the DSC/ABS control.

The automobile 1 having the three functions is capable of securingbehavioral stability of the vehicle.

In the flow shown in FIG. 4 , in step S11 after start of the process,the controller 20 reads a sensor signal. The controller 20 determines atraveling state of the automobile 1. Subsequently, the controller 20executes first processing (step S12). The first processing is related toactive control and switches gear-shifting control according to a roadsurface coefficient of friction (μ). Details of the first processingwill be provided later.

After the first processing in step S12, the process makes a transitionto second processing (step S13) or fourth processing (step S15). Thesecond processing is related to passive control and to gear-shiftingcontrol when the automobile 1 falls into an oversteered state. Detailsof the second processing will be provided later.

After step S13, the process makes a transition to third processing (stepS14) or the fourth processing (step S15). The third processing isrelated to active control and switches gear-shifting control accordingto a slip state of the wheels 2F and 2R. Details of the third processingwill be provided later. In addition, the fourth processing is DSC/ABScontrol. Details of the fourth processing will be provided later.

<First Processing>

FIG. 6 is a flow chart of the first processing. As described earlier,the first processing is related to active control. The first processingis processing which is performed “when the automobile 1 is not in anoversteered state.” By performing the first processing, the controller20 can prevent an occurrence of an oversteered state in advance.

In step S21 after start of the process, the controller 20 determineswhether or not the coefficient of friction of a road surface on whichthe automobile 1 travels is lower than a predetermined threshold(whether or not a determination of Low is made).

The determination in step S21 may be made by comparing the coefficientof friction calculated based on, for example, a vehicle speed, a wheelspeed, a steering angle, and/or a yaw rate with a threshold. Thethreshold which is a comparison object is stored in the controller 20 orthe like in advance. When a result of the determination in step S21 isNo or, in other words, when the coefficient of friction is relativelyhigh, the controller 20, the process advances to step S22. On the otherhand, when the result of the determination in step S21 is Yes or, inother words, when the coefficient of friction is relatively low, theprocess advances to step S25.

When the process advances to step S22, the wheels 2F and 2R arerelatively unlikely to slip. In this case, a grip force of the wheels 2Fand 2R readily stays within the circle of friction and the automobile 1is less likely to fall into a slip state and, eventually, an oversteeredstate. Therefore, the controller 20 executes normal gear-shiftingcontrol as follows.

Specifically, during the regeneration control in a case where thecoefficient of friction is determined to be higher than the threshold,the controller 20 sets the gear-shifting point (downshift point) higherin a state of deceleration of the vehicle during a brake pedal operation(during an operation of the brake pedal 19) than a state of decelerationof the vehicle during a non-brake pedal operation (during anon-operation of the brake pedal 19) under the same condition of thecoefficient of friction.

Specifically, first, in step S22, the controller 20 determines whetheror not the driver is depressing the brake pedal 19 (whether or notbrakes are applied).

The determination in step S22 can be performed based on a signal of thebrake pedal sensor 55. When a result of the determination in step S22 isYes or, in other words, when the driver is depressing the brake pedal 19(when it is determined that a brake pedal operation is being performed),the process advances to step S23. When a result of the determination instep S22 is No or, in other words, when the driver is not depressing thebrake pedal 19 (when it is determined that a non-brake pedal operationis being performed), the process advances to step S24.

When the driver is depressing the brake pedal 19, the controller 20executes regenerative coordination control in which a part of a requiredbraking force of the driver is covered by a regenerative braking torqueof the motor 5. Note that the hydraulic pressure of the friction brakes31 can be reduced by an amount corresponding to the regenerative brakingtorque of the motor 5.

In step S23 to which the process advances when the brake pedal 19 isbeing depressed, the controller 20 selects a first gear-shifting pointS1 as a downshift point of the automatic transmission 8.

FIG. 7 illustrates a downshift point for each shift stage of theautomatic transmission 8. In FIG. 7 , an abscissa represents a vehiclespeed and an ordinate represents the rotation speed of the input shaft 8a of the automatic transmission 8. The first gear-shifting point S1selected in step S23 is set to a constant rotation speed of the inputshaft 8 a regardless of the vehicle speed with respect to each shiftstage. The first gear-shifting point S1 is higher than a secondgear-shifting point S2 and a third gear-shifting point S3 to bedescribed later.

For example, when traveling at the sixth speed, the rotation speed ofthe input shaft 8 a of the automatic transmission 8 reaches the firstgear-shifting point S1 when the vehicle speed is about less than 60km/h. In this case, the automatic transmission 8 shifts down from thesixth speed to the fifth speed. Accompanying the downshift, the rotationspeed of the input shaft 8 a of the automatic transmission 8 or, inother words, the rotation speed of the motor 5 (the output rotationspeed) becomes higher than the first gear-shifting point S1. When thedriver is depressing the brake pedal 19 and the controller 20 isexecuting the regenerative coordination control, the rotation speed ofthe motor 5 performing a regeneration operation can be maintained at ahigh level by setting the downshift point to the first gear-shiftingpoint S1 as compared to a case where the downshift point is set to thesecond gear-shifting point S2 or the third gear-shifting point S3. Ahigh rotation speed of the motor increases a regeneration amount and,therefore, improves the fuel efficiency performance of the automobile 1.

On the other hand, in step S24 to which the process advances when thebrake pedal 19 is not depressed, the controller 20 selects the secondgear-shifting point S2 which is set lower than the first gear-shiftingpoint S1 as the downshift point of the automatic transmission 8.

In other words, when the driver is not depressing the brake pedal 19,the controller 20 does not perform the regenerative coordination controlin the sense that the friction brake system 3 does not contribute towardregeneration. In this case, a regeneration operation is performed byhaving the motor 5 impart a regenerative braking torque corresponding toengine braking to the rear wheels 2R. In a decelerating state where thedriver is not depressing the brake pedal 19, a change to an accelerationrequest may occur when the driver depresses the accelerator pedal 18.When the rotation speed of the input shaft 8 a of the automatictransmission 8 is maintained at a high level due to setting thedownshift point to the first gear-shifting point S1, there is a riskthat a sufficient drive force cannot be secured upon the accelerationrequest by the driver.

In consideration thereof, the controller 20 selects the secondgear-shifting point S2 as the downshift point. As shown in FIG. 7 , thesecond gear-shifting point S2 is set to a constant rotation speed of theinput shaft 8 a regardless of the vehicle speed with respect to eachshift stage in a similar manner to the first gear-shifting point S1. Thesecond gear-shifting point S2 is set lower than the first gear-shiftingpoint S1 regardless of the vehicle speed. The first gear-shifting pointS1 and the second gear-shifting point S2 are both gear-shifting pointswhich are selected when the coefficient of friction is relatively high.Therefore, comparing the first gear-shifting point S1 and the secondgear-shifting point S2 with each other equates to a comparison under thesame condition of the coefficient of friction.

Selecting the second gear-shifting point S2 as the downshift pointrelatively lowers the rotation speed of the input shaft 8 aof theautomatic transmission 8 during deceleration. Accordingly, a sufficientdrive force can be secured during an acceleration request by the driver.

On the other hand, when the process advances to step S25, the wheels 2Fand 2R are likely to slip. In this case, the grip force of the wheels 2Fand 2R is apt to exceed the circle of friction and the behavior of theautomobile 1 tends to become unstable. The controller 20 executescontrol for preventing the behavior of the automobile 1 from becomingunstable due to a gear-shifting operation of the automatic transmission8.

Specifically, first, in step S25, the controller 20 determines whetheror not the automobile 1 is accelerating. When a result of thedetermination in step S25 is Yes (in other words, when it is determinedthat the automobile 1 is accelerating), the process advances to stepS26. On the other hand, when a result of the determination in step S25is No (in other words, when it is determined that the automobile 1 isdecelerating), the process advances to step S27.

In this case, in step S26 or, during acceleration of the vehicle when itis determined that the coefficient of friction is lower than thethreshold, the controller 20 limits an upshift which causes the shiftstage to be changed to a predetermined stage or higher.

Specifically, when the automobile 1 is accelerating, the automatictransmission 8 performs an upshift as the vehicle speed and/or therotation speed of the input shaft 8 a of the automatic transmission 8increases. The accelerating automobile 1 eventually makes a transitionto deceleration. When such a transition to deceleration is made, theautomatic transmission 8 is to perform a downshift accompanying thedeceleration. During a downshift of the automatic transmission 8, atorque fluctuation of the rear wheels 2R occurs due to a moment ofinertia of the automatic transmission 8. When the coefficient offriction is low, there is a risk that the torque fluctuation of the rearwheels 2R which accompanies the downshift may make the behavior of theautomobile 1 unstable. In consideration thereof, the controller 20limits an upshift in step S26.

Specifically, the controller 20 prohibits upshifts which cause the shiftstage to be changed to the seventh and higher speeds such as an upshiftfrom the sixth speed to the seventh speed and an upshift from theseventh speed to the eighth speed. Therefore, when the process advancesto step S26, the automatic transmission 8 is temporarily shifted up tothe sixth speed at a maximum. By limiting a highest-speed stage of theautomatic transmission 8, consequently, a frequency of downshifts when atransition is made from acceleration to deceleration can be reduced.Accordingly, opportunities for the behavior of the automobile 1 tobecome unstable such as an occurrence of oversteering decrease.

On the other hand, in step S27 or, in other words, during decelerationof the vehicle when it is determined that the coefficient of friction islower than the predetermined threshold in the regeneration control, thecontroller 20 sets the downshift point lower than during deceleration ofthe vehicle when it is determined that the coefficient of friction isequal to or higher than the threshold.

Specifically, when the automobile 1 is decelerating, the automatictransmission 8 performs a downshift as the vehicle speed and/or therotation speed of the input shaft 8 a of the automatic transmission 8decreases. In order to avoid, as much as possible, destabilization ofthe behavior of the automobile 1 which is attributable to the downshift,the controller 20 performs the downshift in a state where the vehiclespeed is as low as possible.

Specifically, the controller 20 selects the third gear-shifting point S3which is set lower than both the first gear-shifting point S1 and thesecond gear-shifting point S2 as a downshift point of the automatictransmission 8. As shown in FIG. 7 , the third gear-shifting point S3 isset to a constant rotation speed of the input shaft 8 a regardless ofthe vehicle speed with respect to each shift stage in a similar mannerto the first gear-shifting point S1 and the second gear-shifting pointS2. The third gear-shifting point S3 is set lower than the firstgear-shifting point S1 and the second gear-shifting point S2 regardlessof the vehicle speed. Comparing the first gear-shifting point S1 and thesecond gear-shifting point S2 with the third gear-shifting point S3equates to a comparison under different conditions of the coefficient offriction.

As described earlier, the highest-speed stage is limited to the sixthspeed when a transition is made from acceleration to deceleration. Inaddition, the downshift point is the third gear-shifting point S3 whichis set relatively low. Therefore, in step S27, the automatictransmission 8 does not perform a downshift until the vehicle speeddecreases to around 40 km/h as indicated by a blank arrow in FIG. 7 .Since a downshift at a high vehicle speed is not performed, the behaviorof the automobile 1 can be prevented from becoming unstable.

Next, when, after the downshift point is set to the third gear-shiftingpoint based on the coefficient of friction, the rotation speed of theinput shaft 8 adecreases to the third gear-shifting point, thecontroller 20 interrupts motive power transmission between the inputshaft 8 a and the output shaft 8 b.

Specifically, in step S28 which follows step S27, the controller 20opens the K1 clutch in response to the rotation speed of the input shaft8 a of the automatic transmission 8 falling to the third gear-shiftingpoint S3. As described earlier, the K1 clutch is a clutch made up offriction fastening elements of the automatic transmission 8. When the K1clutch is opened, the motive power transmission between the input shaft8 a and the output shaft 8 b of the automatic transmission 8 isinterrupted. Since opening of the K1 clutch reduces a torque which actson the rear wheels 2R, destabilization of the behavior of the automobile1 can be suppressed and, at the same time, engine stall due to a furtherdecrease in the rotation speed of the engine 4 can be avoided.

After active control when the coefficient of friction is low, theprocess makes a transition to the fourth processing.

As will be described later in the fourth processing, when an unstablebehavior of the automobile 1 diverges after interrupting the motivepower transmission between the input shaft 8 a and the output shaft 8 bin step S28, the controller 20 causes the friction brake system 3 toexecute a control (DSC/ABS control) for stabilizing the behavior of theautomobile 1 by imparting a braking force to the front wheels 2F or therear wheels 2R.

In this case, FIG. 3B is a block diagram for explaining a base set of agear-shifting point.

The controller 20 is configured such that, during normal operations (forexample, when there is no risk of the behavior of the automobile 1becoming unstable such as an oversteered state), a downshift pointcorresponding to an operational state of the automobile 1 isappropriately set by referring to gear-shifting maps M1 to M3 whichdefine a base set of downshift points.

In particular, the controller 20 according to the present embodiment isconfigured to select one of a plurality of gear-shifting maps based onthe operational state of the automobile 1. For example, the plurality ofgear-shifting maps are stored in the memory and used by being read bythe controller 20 when appropriate.

Specifically, as shown in FIG. 3B, the controller 20 is configured torefer to a regeneration request map M3, a combustion request map Ml, anda travel request map M2 as the plurality of gear-shifting maps. Theregeneration request map M3 corresponds to a map (a third map) which isused during the regenerative coordination control or, in other words,when the friction brake system 3 and the motor 5 perform decelerativeregeneration by working in a coordinated manner.

The combustion request map M1 and the travel request map M2 are mapsused during non-regenerative coordination control or, in other words,during the second regeneration control to be described later. Forexample, the maps are used during acceleration of the automobile 1 andwhen decelerative regeneration is solely performed by the motor 5without involving the friction brake system 3. The combustion requestmap M1 corresponds to a map (first map) which is used during anon-operation of the accelerator pedal 18 (during decelerativeregeneration solely by the motor 5) and the travel request map M2corresponds to a map (second map) which is used during an operation ofthe accelerator pedal 18.

The maps are at least related to a downshift among a downshift and anupshift and define a plurality of gear-shifting points which correspondto each shift stage. Each gear-shifting point indicates a threshold ofthe rotation speed of the input shaft 8 a which triggers gear-shifting.

In the regeneration request map M3, each gear-shifting point is definedon a high-rotation-speed side than both the combustion request map M1and the travel request map M2. In other words, in the regenerationrequest map M3, the rotation speed of the input shaft 8 a is set so asto be kept high as compared to both the combustion request map M1 andthe travel request map M2.

On the other hand, in the combustion request map M1, each gear-shiftingpoint is defined on a further low-rotation-speed side than the travelrequest map M2. In other words, in the travel request map M2, while therotation speed of the input shaft 8 a is kept lower than theregeneration request map M3, the rotation speed of the input shaft 8 ais kept higher than the combustion request map M1.

The controller 20 uses gear-shifting points defined in each map as abase set of gear-shifting points. In addition, when specific conditionsare satisfied in the first processing, the first gear-shifting point S1,the second gear-shifting point S2, and the third gear-shifting point S3described earlier are to be used in place of such a base set.

Specifically, when the process advances to step S28, the downshift pointis set to the third gear-shifting point S3 instead of a value of a baseset defined in each map. In a similar manner, when the process advancesto step S23, the controller 20 sets the downshift point to the firstgear-shifting point S1 instead of a value of a base set defined in eachmap. When the process advances to step S24, the downshift point is setto the second gear-shifting point S2 instead of a value of a base setdefined in each map. The first gear-shifting point S1, the secondgear-shifting point S2, and the third gear-shifting point S3 are set soas to assume same values for each map regardless of which of the threemaps has been referred to by the controller 20.

<Second Processing>

FIG. 8 is a flow chart of the second processing. As described earlier,the second processing is passive control. In step S31 after start of theprocess, the controller 20 determines whether or not a determination ofoversteering has been made. For example, the controller 20 determineswhether or not the automobile 1 is in an oversteered state based on adeviation between an estimated yaw rate which can be calculated from thevehicle speed and the steering angle and an actual yaw rate based on asignal of the yaw rate sensor 54. The controller 20 may determine thatthe automobile 1 is in an oversteered state when the deviation betweenthe estimated yaw rate and the actual yaw rate is equal to or largerthan a predetermined value. When a result of the determination in stepS31 is No or, in other words, when the automobile 1 is not in anoversteered state, passive control is not performed. The processadvances to the third processing. On the other hand, when the result ofthe determination in step S31 is Yes or, in other words, when theautomobile 1 is in an oversteered state, the process advances to stepS32.

In step S32, the controller 20 determines whether or not brakeregeneration is being performed. In other words, a determination ofwhether or not the driver is depressing the brake pedal 19 is made. Whena result of the determination in step S32 is Yes, the process makes atransition to step S33, but when the result of the determination in stepS32 is No, the process advances to step S34 without making a transitionto step S33.

As described earlier, during deceleration when the driver is depressingthe brake pedal 19, the regenerative coordination control in which apart of a required braking force of the driver is covered by aregenerative braking torque of the motor 5 is executed. The regenerativebraking torque of the motor 5 is only imparted to the rear wheels 2R ofthe automobile 1 which is a rear-wheel drive vehicle. Therefore, alateral force of the rear wheels 2R decreases and the behavior of theautomobile 1 is apt to fall into an oversteered state.

In consideration thereof, in step S33, the controller 20 executestorque-increase control. Specifically, an input torque of the inputshaft 8 a of the automatic transmission 8 is increased so as toeliminate the regenerative braking torque of the motor 5 having so farcovered for a part of the braking force of the friction brakes 31. Thetorque-increase control corresponds to an end of the regenerativecoordination control. The friction brake system 3 compensates for abraking force corresponding to the eliminated regenerative brakingtorque by the braking force of the friction brakes 31. Note that evenafter the regenerative coordination control ends, a regenerative brakingtorque corresponding to engine braking which accompanies releasing theaccelerator remains and the regeneration operation of the motor 5 itselfcontinues. Since a regeneration amount is secured even when theautomobile 1 is in an oversteered state, an advantage is gained in termsof improving fuel efficiency performance of the automobile 1.

Since the regenerative braking torque having been imparted to the rearwheels 2R decreases and a lateral force of the rear wheels 2R issecured, the oversteered state of the automobile 1 moves towardresolution. The deviation between the estimated yaw rate and the actualyaw rate moves toward reduction. Stabilization of the behavior of theautomobile 1 can be achieved while securing as much of a regenerationamount as possible. After step S33, the process advances to step S34.

Note that when brake regeneration is not performed or, in other words,during deceleration where the driver is not depressing the brake pedal19 in step S32, since second regeneration control of performingregeneration control corresponding to engine braking is being performedand regenerative coordination control is not being performed, the torqueincrease in step S33 is not performed. Even when the process makes atransition from step S32 to step S34, the motor 5 performs aregeneration operation with a regenerative braking torque correspondingto engine braking which accompanies releasing the accelerator.

In step S34, the controller 20 determines whether or not an unstablebehavior of the automobile 1 is diverging. For example, the controller20 may determine that the unstable behavior of the automobile 1 isdiverging when the deviation between the estimated yaw rate and theactual yaw rate is expanding. When a result of the determination in stepS34 is Yes, the process makes a transition to step S35. When the resultof the determination in step S34 is No, the process makes a transitionto step S310.

In step S35, the controller 20 determines whether or not the automatictransmission 8 is not gear-shifting (in other words, non-gear-shifting).When the automatic transmission 8 is not gear-shifting (in other words,in a case of Yes), the process advances to step S36. When the automatictransmission 8 is gear-shifting (in other words, in a case of No), theprocess advances to step S310.

In step S36, the controller 20 delays a downshift of the automatictransmission 8. In other words, the controller 20 prohibits a downshiftof the automatic transmission 8 until the oversteered state of theautomobile 1 is resolved even if the traveling state of the automobile 1has reached a downshift point. Since a downshift of the automatictransmission 8 accompanies a torque fluctuation of the rear wheels 2Rand there is a risk that the behavior of the automobile 1 is furtherdestabilized as described earlier, prohibiting a downshift prevents thebehavior of the automobile 1 from becoming further unstable. Note thatthe downshift point is the first gear-shifting point S1 or the secondgear-shifting point S2 in normal gear-shifting control.

In subsequent step S37, the controller 20 determines whether or not theoversteered state of the automobile 1 has been resolved. The controller20 may determine that the oversteered state of the automobile 1 has beenresolved when the deviation between the estimated yaw rate and theactual yaw rate falls below the predetermined value. When theoversteered state of the automobile 1 has been resolved, the processadvances to the fourth processing. When the oversteered state of theautomobile 1 has not been resolved, the process advances to step S38.

In step S38, the controller 20 determines whether or not the rotationspeed of the input shaft 8 a of the automatic transmission 8 has reachedthe third gear-shifting point S3. When the rotation speed of the inputshaft 8 a has reached the third gear-shifting point S3, the processadvances to step S39, but when the rotation speed of the input shaft 8 ahas not reached the third gear-shifting point S3, the process advancesto the fourth processing. As described earlier, the third gear-shiftingpoint S3 is a downshift point which takes an engine stall intoconsideration.

In step S39, the controller 20 opens the K1 clutch of the automatictransmission 8 in a similar manner to step S28 of the first processing.Accordingly, an engine stall can be suppressed. Subsequently, theprocess advances to the fourth processing.

In this manner, when the automobile 1 falls into an oversteered stateduring deceleration by the regenerative coordination control or thesecond regeneration control, a downshift of the automatic transmission 8is delayed. Behavior of the automobile 1 is prevented from becomingfurther unstable due to the downshift. In addition, while the rotationspeed of the input shaft 8 a of the automatic transmission 8 decreasesand a risk of an engine stall arises when a downshift of the automatictransmission 8 is delayed, since motive power transmission between theinput shaft 8 a and the output shaft 8 b of the automatic transmission 8is interrupted once the rotation speed of the input shaft 8 a of theautomatic transmission 8 reaches the limited rotation speed (in otherwords, the third gear-shifting point S3), an engine stall can besuppressed.

On the other hand, when the automobile 1 is in an oversteered state andthe automatic transmission 8 is performing a downshift (a case where theresult of step S35 is No) or when a delayed downshift is performed afterthe oversteered state of the automobile 1 is resolved (a case where theresult of step S34 is No), the controller 20 executes gear-shiftingcontrol upon a determination of oversteering in step S310. Details ofthe gear-shifting control will be provided later. In simple terms, atorque of the rear wheels 2R fluctuates due to inertia of the automatictransmission 8 which accompanies a downshift. In the gear-shiftingcontrol upon a determination of oversteering in step S310, an inputtorque of the input shaft 8 a of the automatic transmission 8 isincreased as compared to during normal gear-shifting control or, inother words, an input torque during a non-determination of oversteeringso that a torque fluctuation of the rear wheels 2R corresponding to theamount of inertia is suppressed. As a result of a relative increase inan amount of increase of the input torque, a torque fluctuation issuppressed even when a downshift is performed and destabilization of thebehavior of the automobile 1 attributable to the downshift is preventedfrom deteriorating.

In subsequent step S311, the controller 20 determines whether or notbrake regeneration is being performed, and when a result of thedetermination is Yes meaning that brake regeneration is being performed,the process advances to step S312. On the other hand, when the result ofthe determination is No meaning that brake regeneration is not beingperformed, the process advances from step S311 to the fourth processing.

In step S312, the controller 20 stops the regenerative coordinationcontrol, secures, with the friction brakes 31, the braking force havingbeen covered by the regenerative braking torque of the motor 5, andachieves deceleration commensurate with braking requested by the driver.Note that even after the regenerative coordination control ends, aregenerative braking torque corresponding to engine braking whichaccompanies releasing the accelerator remains and the regenerationoperation of the motor 5 itself continues.

<Gear-Shifting Processing>

FIG. 9 is a flow chart of gear-shifting control. In step S41 after startof the process, the controller 20 reads an AT input torque and the ATinput rotation speed. The process subsequently advances to each of stepS42 and step S44.

In step S42, the controller 20 sets a target acceleration fluctuationduring gear-shifting of the automatic transmission 8. The targetacceleration fluctuation is a target value of an accelerationfluctuation which is created in the automobile 1 during gear-shifting ofthe automatic transmission 8. Basically, the target accelerationfluctuation is set such that the higher the AT input rotation speed, thelarger the target acceleration fluctuation. When the AT input rotationspeed is high, causing the driver to feel an upshift or a downshift isallowed. The target acceleration fluctuation is determined according toa shift stage and the AT input rotation speed of the automatictransmission 8 based on a relational expression or a map set withrespect to each of an upshift and a downshift.

In subsequent step S43, the controller 20 calculates an AT output torquefrom the set target acceleration fluctuation. The AT output torque is atorque fluctuation of the output shaft 8 b during gear-shifting of theautomatic transmission 8.

On the other hand, in step S44, the controller 20 sets a targetgear-shifting time during gear-shifting of the automatic transmission 8.Basically, the target gear-shifting time is set such that the higher theAT input rotation speed, the shorter the target gear-shifting time. Whenthe AT input rotation speed is high, it is required that an upshift or adownshift be promptly completed. The target gear-shifting time isdetermined from the shift stage and the AT input rotation speed of theautomatic transmission 8 based on a relational expression or a map setwith respect to each of an upshift and a downshift.

In subsequent step S45, the controller 20 calculates an AT inputrotation gradient from the set target gear-shifting time. The AT inputrotation gradient is a change rate of the rotation speed of the inputshaft 8 a during gear-shifting of the automatic transmission 8.

After step S43 and step S45, the process makes a transition to step S46.In step S46, the controller 20 determines whether or not a correction ofthe calculated AT output torque and/or the calculated AT input rotationgradient is necessary. When the automobile 1 performs gear-shifting inan oversteered state as in step S310 of the second processing describedearlier, a torque fluctuation of the rear wheels 2R which accompanies adownshift must be suppressed in order to stabilize the behavior of theautomobile 1. In this case, in step S46, the controller 20 determinesthat a correction is necessary. When a result of the determination instep S46 is Yes, the process advances to step S47 and a correction ofthe calculated AT output torque and/or the calculated AT input rotationgradient is performed. Specifically, in gear-shifting control upon adetermination of oversteering, a correction is performed so that thetorque fluctuation of the rear wheels 2R is suppressed or, in otherwords, the AT output torque becomes flat. During a determination of anoversteered state, the target acceleration fluctuation is set smallerthan during a non-determination of an oversteered state. After thecorrection, the process advances to step S48. On the other hand, when aresult of the determination in step S46 is No or, in other words, innormal gear-shifting control where a correction is unnecessary, theprocess advances to step S48 instead of advancing to step S47.

Note that even in first coordinated gear-shifting control in step S54and in second coordinated gear-shifting control in step S55 of the thirdprocessing to be described later, the correction of step S47 is executedand the torque fluctuation of the rear wheels 2R during gear-shifting issuppressed.

In step S48, the controller 20 calculates the AT input torque based onthe AT output torque and the AT input rotation gradient. The AT inputtorque is a torque input to the input shaft 8 a of the automatictransmission 8 and the AT input torque is mainly adjusted by the motor5. When performing a downshift in step S310 of the second processingdescribed earlier, as a result of the correction in step S47 beingperformed, an amount of increase of the AT input torque is increased ascompared to an amount of increase during a normal downshift (in otherwords, during a non-determination of an oversteered state and withoutany correction).

Once the AT input torque is calculated, in subsequent step S49, thecontroller 20 calculates hydraulic pressure to be supplied to thefriction fastening elements of the automatic transmission 8 so as tocorrespond to the calculated AT input torque. According to the sethydraulic pressure, the automatic transmission 8 performs a downshift oran upshift due to the friction fastening elements being supplied withthe hydraulic pressure.

<Third Processing>

FIG. 10 is a flow chart of the third processing. As described earlier,the third processing is active control. In step S51 after start of theprocess, the controller 20 determines whether or not a slipdetermination has been made. The controller 20 may determine a slipstate of each of the wheels 2F and 2R based on, for example, the vehiclespeed and the wheel speed. When a result of the determination in stepS51 is Yes or, in other words, when it is determined that the wheels 2Fand 2R are slipping, the process advances to step S52, and when theresult of the determination in step S51 is No or, in other words, whenit is determined that the wheels 2F and 2R are not slipping, the processadvances to step S53.

In step S53, the controller 20 determines whether or not a turndetermination has been made. The controller 20 may determine a turnstate of the automobile 1 based on, for example, the steering angle andthe yaw rate. When a result of the determination in step S53 is Yes or,in other words, when it is determined that the automobile 1 is in a turnstate, the process advances to step S52, and when the result of thedetermination in step S53 is No or, in other words, when it isdetermined that the automobile 1 is not in a turn state, the processadvances to step S56.

In step S56, the controller 20 executes normal gear-shifting control. Inother words, since the wheels 2F and 2R are not in a slip state and theautomobile 1 is in a state of straight travel, it is unlikely that theautomobile 1 will become unstable during gear-shifting of the automatictransmission 8. In step S56, the correction of step S47 in the flow ofthe gear-shifting control shown in FIG. 9 is not performed.

On the other hand, in steps S52, S54, and S55, the wheels 2F and 2R arein a slip state or the automobile 1 is in a turn state, and when theautomatic transmission 8 performs gear-shifting in this state and atorque of the rear wheels 2R fluctuates, there is a risk that thebehavior of the automobile 1 may become unstable. In considerationthereof, the controller 20 performs control for preventing the behaviorof the automobile 1 from becoming unstable.

First, in step S52, the controller 20 determines whether or not brakeregeneration is being performed. When the result of the determination isYes meaning that brake regeneration is being performed, the processadvances to step S54. On the other hand, when the result of thedetermination is No meaning that brake regeneration is not beingperformed, the process advances to step S55.

When brake regeneration is being performed, the controller 20 executescoordinated control of the friction brake system 3, the motor 5, and theautomatic transmission 8. Specifically, in step S54, the automatictransmission 8 executes gear-shifting control so that the torquefluctuation of the rear wheels 2R which accompanies gear-shifting issuppressed. In step S54, the correction of step S47 in the flow of thegear-shifting control shown in FIG. 9 is performed. In addition, thefriction brake system 3 and/or the motor 5 impart a torque to the rearwheels 2R so as to compensate for the torque fluctuation duringgear-shifting. As a result, the behavior of the automobile 1 isprevented from becoming unstable.

When brake regeneration is not being performed, the controller 20executes coordinated control of the motor 5 and the automatictransmission 8. In step S55, the automatic transmission 8 executesgear-shifting control so that the torque fluctuation of the rear wheels2R which accompanies gear-shifting is suppressed. Even in step S55, thecorrection of step S47 in the flow of the gear-shifting control shown inFIG. 9 is performed. In addition, the motor 5 imparts a torque to therear wheels 2R so as to compensate for the torque fluctuation duringgear-shifting. As a result, the behavior of the automobile 1 isprevented from becoming unstable.

After the third processing, the process advances to the fourthprocessing.

<Fourth Processing>

FIG. 11 is a flow chart of the fourth processing. The fourth processingis DSC/ABS control. In step S61 after the start of the process, thecontroller 20 determines whether or not an unstable behavior of theautomobile 1 is diverging. When an unstable behavior of the automobile 1is diverging, the process advances to step S62. When an unstablebehavior of the automobile 1 is not diverging, since DSC/ABS control isunnecessary, the fourth processing is ended.

In step S62, the controller 20 determines whether or not brakes areapplied. When the driver is depressing the brake pedal 19 (in otherwords, when the result of the determination is Yes), the processadvances to step S63, but when the driver is not depressing the brakepedal 19 (in other words, when the result of the determination is No),the process advances to step S64.

In step S63, since the brakes are applied, DSC control or ABS control isexecuted to cause the unstable behavior of the automobile 1 to converge.In step S64, since the brakes are not applied, DSC control is executedto cause the unstable behavior of the automobile 1 to converge.

Once the unstable behavior of the automobile 1 converges due to controlintervention in step S63 or step S64, the fourth processing ends.

<Control Example>

Next, the second processing will be described with reference to timecharts shown in FIGS. 12 to 14 . Each time chart includes changes in abrake pedal operation amount and brake fluid pressure, a change in asteering angle (a measured value of the steering angle sensor 53), achange in a gear stage, a change in a yaw rate (a measured value of theyaw rate sensor 54), a change in a regenerative braking torque, a changein the AT input torque, a change in a transmission ratio of theautomatic transmission 8, and a change in the AT input rotation speed.

First, FIG. 12 is a time chart in a case where a downshift of theautomatic transmission 8 is prohibited until an oversteered state of theautomobile 1 is resolved. At a time t1, the driver starts to depress thebrake pedal 19. The controller 20 starts regenerative coordinationcontrol. Based on a signal from the controller 20, the friction brakesystem 3 reduces brake fluid pressure with respect to an operationamount of the brake pedal 19 which is indicated by a long dashed dottedline. A braking force of the friction brakes 31 decreases by acorresponding amount. The motor 5 increases a regenerative brakingtorque so as to compensate for the decreased amount of the braking forceof the friction brakes 31. Accordingly, since regenerative energy can besecured, an advantage is gained in terms of improving fuel efficiency ofthe automobile 1. Since the regenerative braking torque increases, atorque input to the input shaft 8 a of the automatic transmission 8decreases.

At a time t2, the driver starts to steer the steering wheel 110.Accordingly, the steering angle gradually increases. The automobile 1starts to turn and the yaw rate gradually increases.

At a time t3, the automobile 1 reaches an oversteered state and adeviation between an actual yaw rate and an estimated yaw rateincreases. In order to end the regenerative coordination control, thecontroller 20 increases the input torque of the input shaft 8 a of theautomatic transmission 8 so as to eliminate the regenerative brakingtorque of the motor 5 having so far covered for a part of the brakingforce of the friction brakes 31 (torque increase, step S33).Accordingly, the regenerative braking torque decreases. Note that evenat the time t3 and thereafter, the regenerative braking torquecorresponding to engine braking which accompanies releasing theaccelerator remains and the regeneration operation of the motor 5 itselfcontinues. In addition, the hydraulic pressure of the friction brakes 31is increased so as to compensate for the decrease in the regenerativebraking torque of the motor 5.

As the automobile 1 decelerates, the AT input rotation speed graduallydecreases. At the time t3 or thereafter, even if the AT input rotationspeed reaches the first gear-shifting point S1 or, in other words, agear-shifting point which is set in the case of regenerativecoordination control, the controller 20 does not allow the automatictransmission 8 to execute a downshift. A downshift of the automatictransmission 8 is delayed (step S36).

Since the regenerative braking torque having been imparted to the rearwheels 2R decreases and a lateral force of the rear wheels 2R is secureddue to the torque increase described earlier, the oversteered state ofthe automobile 1 moves toward resolution. At a time t4, when theoversteered state of the automobile 1 is resolved, the controller 20causes the automatic transmission 8 to execute the downshift which hasbeen delayed (a transition from step S34 to step S310). Specifically,the input torque of the input shaft 8 a of the automatic transmission 8is increased as compared to during normal gear-shifting control byincreasing the torque of the motor 5 (refer to arrow indicating“increase”). Accordingly, since a torque fluctuation of the rear wheels2R corresponding to an inertia during the downshift is suppressed, thebehavior of the automobile 1 can be prevented from becoming unstableonce again immediately after the resolution of the oversteered state.

In addition, at a time t5, the downshift of the automatic transmission 8ends.

Note that during a downshift of the automatic transmission 8 after theresolution of the oversteered state of the automobile 1, normalgear-shifting control may be executed instead of gear-shifting controlupon a determination of oversteering. In other words, an increase in thetorque of the motor 5 during the downshift may be suppressed.

FIG. 13 is a time chart in a case where a downshift of the automatictransmission 8 is prohibited until an oversteered state of theautomobile 1 is resolved. The time chart in FIG. 13 differs from thetime chart in FIG. 12 in that the AT input rotation speed reaches thethird gear-shifting point S3.

Even in the time chart in FIG. 13 , the driver starts depressing thebrake pedal 19 at the time t1, the driver starts to steer the steeringwheel 110 at the time t2, and the automobile 1 reaches an oversteeredstate at the time t3 in a similar manner to the time chart in FIG. 12 .In order to end the regenerative coordination control, the controller 20increases the input torque of the input shaft 8 a of the automatictransmission 8 so as to eliminate the regenerative braking torque of themotor 5 having so far covered for a part of the braking force of thefriction brakes 31 (torque increase). Accordingly, the regenerativebraking torque decreases. Note that even at the time t3 and thereafter,the regeneration operation of the motor 5 itself continues.Gear-shifting of the automatic transmission 8 is delayed.

As the automobile 1 decelerates, the AT input rotation speed graduallydecreases and, at the time t4, the AT input rotation speed reaches thethird gear-shifting point S3. The third gear-shifting point S3 is adownshift point which takes an engine stall into consideration. Thecontroller 20 opens the K1 clutch of the automatic transmission 8.Accordingly, the AT input rotation speed decreases and a transmissionratio which is a velocity ratio between the input shaft 8 a and theoutput shaft 8 b of the automatic transmission 8 decreases.

Note that the oversteered state is resolved by a torque increase of theinput shaft 8 a. After the resolution of the oversteered state, theautomatic transmission 8 performs a downshift.

FIG. 14 is a time chart in a case where the automobile 1 reaches anoversteered state during gear-shifting of the automatic transmission 8.Even in the time chart in FIG. 14 , the driver starts depressing thebrake pedal 19 at the time t1 and the driver starts to steer thesteering wheel 110 at the time t2 in a similar manner to the time chartin FIG. 12 . The controller 20 performs regenerative coordinationcontrol.

At the time t3, since the AT input rotation speed has reached the firstgear-shifting point S1, the automatic transmission 8 executes adownshift. Since the automobile 1 is turning, the first coordinatedgear-shifting control of the third processing (step S54) is executed. Asillustrated in FIG. 14 , the hydraulic pressure of the friction brakes31 is adjusted at the time t4 or thereafter in accordance with thedownshift of the automatic transmission 8.

At the time t5 during the gear-shifting, the automobile 1 reaches anoversteered state. As in steps S310 to S312 in the second processing, inorder to stop the regenerative coordination control, the controller 20increases the input torque of the input shaft 8 a of the automatictransmission 8 (torque increase) and, at the same time, increases theinput torque of the input shaft 8 a of the automatic transmission 8 ascompared to during normal gear-shifting control by increasing the torqueof the motor 5. The torque increase for stopping the regenerativecoordination control and the torque increase for gear-shifting may besubstantially performed at the same time or performed at staggeredtimings. By securing a lateral force of the rear wheels 2R andsuppressing a torque fluctuation during gear-shifting, destabilizationof the behavior of the automobile 1 is prevented from deteriorating.Note that the hydraulic pressure of the friction brakes 31 is increasedso as to compensate for the decrease in the regenerative braking torqueof the motor 5. In addition, the motor 5 performs a regenerationoperation with a regenerative braking torque corresponding to enginebraking.

Subsequently, at a time t6, the downshift of the automatic transmission8 ends.

(Modification)

FIG. 15 shows a modification of the second processing. The modificationdiffers from the flow in FIG. 8 in that a downshift is not delayed. Instep S71 after start of the process, the controller 20 determineswhether or not a determination of oversteering has been made. When aresult of the determination in step S71 is No, passive control is notperformed. When a result of the determination in step S71 is Yes, theprocess advances to step S72.

In step S72, the controller 20 determines whether or not brakeregeneration is being performed. When a result of the determination instep S72 is Yes, the process makes a transition to step S73, but whenthe result of the determination in step S72 is No, the process advancesto step S74 without making a transition to step S73.

In step S73, the controller 20 executes torque-increase control.Accordingly, the regenerative coordination control ends. Since theregenerative braking torque having been imparted to the rear wheels 2Rdecreases and a lateral force of the rear wheels 2R is secured, theoversteered state of the automobile 1 moves toward resolution. Afterstep S73, the process advances to step S74. In step S74 or thereafter,the motor 5 performs a regeneration operation with a regenerativebraking torque corresponding to engine braking which accompaniesreleasing the accelerator. Even when the automobile 1 is in anoversteered state, since as much of a regeneration amount as possible issecured, an advantage is gained in terms of improving fuel efficiencyperformance of the automobile 1.

In step S74, the controller 20 determines whether or not an unstablebehavior of the automobile 1 is diverging. When a result of thedetermination in step S74 is Yes, the process makes a transition to stepS75. When the result of the determination in step S74 is No, the processmakes a transition to step S710.

In step S75, the controller 20 determines whether or not the automatictransmission 8 is not gear-shifting. When the automatic transmission 8is not gear-shifting (in other words, in a case of Yes), the processadvances to step S76. When the automatic transmission 8 is gear-shifting(in other words, in a case of No), the process advances to step S710.

In step S76, the controller 20 determines whether or not the rotationspeed of the input shaft 8 a of the automatic transmission 8 has reachedthe first gear-shifting point S1. When the rotation speed of the inputshaft 8 a has reached the first gear-shifting point S1, the processadvances to step S77, but when the rotation speed of the input shaft 8 ahas not reached the first gear-shifting point S1, the process advancesto the fourth processing. As described earlier, the first gear-shiftingpoint S1 is a downshift point when regenerative coordination control isbeing executed. Note that in step S76, the controller 20 may determinewhether or not the rotation speed of the input shaft 8 a of theautomatic transmission 8 has reached the second gear-shifting point S2.

In step S77, the controller 20 opens the K1 clutch of the automatictransmission 8. Since a downshift of the automatic transmission 8 is notperformed, destabilization of the behavior of the automobile 1attributable to the downshift is suppressed.

In this manner, in the second processing according to the modification,when the automobile 1 is in an oversteered state, the K1 clutch isopened and a downshift of the automatic transmission 8 is not performed.Accordingly, the behavior of the automobile 1 is prevented from becomingfurther unstable due to gear-shifting. In addition, an engine stall canbe avoided.

On the other hand, when the automobile 1 is in an oversteered state andthe automatic transmission 8 is performing a downshift (a case where theresult of step S75 is No) or when a downshift is performed after theoversteered state of the automobile 1 is resolved (a case where theresult of step S74 is No), the controller 20 executes gear-shiftingcontrol upon a determination of oversteering in step S710. Since atorque fluctuation is suppressed even when a downshift is performed,destabilization of the behavior of the automobile 1 is prevented fromdeteriorating.

In subsequent step S711, the controller 20 determines whether or notbrake regeneration is being performed, and when a result of thedetermination is Yes meaning that brake regeneration is being performed,the process advances to step S712. On the other hand, when the result ofthe determination is No meaning that brake regeneration is not beingperformed, the process advances from step S711 to the fourth processing.

In step S712, the controller 20 stops the regenerative coordinationcontrol, secures, with the friction brakes 31, the braking force havingbeen covered by the regenerative braking torque of the motor 5, andachieves deceleration commensurate with braking requested by the driver.

Note that the disclosed technique is not limited to the embodimentdescribed above and also includes various other configurations. Forexample, the configuration of the automobile 1 is illustrative. Theconfiguration can be appropriately modified according to specifications.

In each of the flows shown in FIGS. 4, 6, 8 to 11, and 15 , an order ofthe steps can be rearranged, a part of the steps can be omitted, orother steps can be added.

(Summary)

As described above, according to the present embodiment, regenerationcontrol is executed by causing the motor 5 to perform a regenerationoperation at least during deceleration of the automobile 1. Due to theregeneration control, regenerative energy accumulated in thehigh-voltage battery 9 increases. A regenerative braking torque producedby the motor 5 is only imparted to the rear wheels 2R through theautomatic transmission 8.

In addition, during deceleration of the automobile 1, the controller 20as the controller outputs a gear-shifting signal according to therotation speed of the input shaft 8 a to the automatic transmission 8,triggered by the rotation speed of the input shaft 8 a decreasing to apredetermined downshift point. The automatic transmission 8 receives thegear-shifting signal and changes the shift stage or, in other words,executes a downshift of changing the shift stage from a high-speed stageto a low-speed stage. During deceleration of the automobile 1, a shiftstage corresponding to an operational state of the engine 4 is selected.

In addition, during deceleration of the vehicle when it is determinedthat the coefficient of friction is equal to or higher than thepredetermined threshold, the controller 20 sets the downshift point tothe first gear-shifting point S1 or the second gear-shifting point S2which are relatively high. When the coefficient of friction is high, anoccurrence of an oversteered state is suppressed even when adopting aconfiguration in which a downshift starts on a high-rotation-speed side.Since a regeneration operation on a high-rotation-speed side enables aregeneration amount to be increased as compared to a low-rotation-speedside, a contribution is made toward improving fuel efficiencyperformance.

On the other hand, during deceleration of the vehicle when it isdetermined that the coefficient of friction is lower than thepredetermined threshold, the controller 20 sets the downshift point tothe relatively low third gear-shifting point S3 so that a downshift isstarted at a later timing. Accordingly, the gear-shifting control can bestarted after an oversteered state is avoided or, even if an oversteeredstate has occurred, the gear-shifting control can be started after theoversteered state is resolved. As a result, the behavior of theautomobile 1 can be stabilized and robustness of the vehicle can beimproved.

As described above, the gear-shifting control apparatus according to thepresent embodiment is capable of achieving both securement of as much ofa regeneration amount as possible due to a regeneration operation on ahigh-rotation-speed side and an improvement in robustness due todelaying a start timing of gear-shifting control.

In addition, as described with reference to step S26 in FIG. 6 , duringacceleration of the vehicle when the coefficient of friction isrelatively low, a limitation is to be imposed on a highest stage of theshift stages. Accordingly, when the automobile 1 makes a transition fromacceleration to deceleration, a frequency of occurrences of a downshiftcan be reduced. As a result, opportunities where oversteering may occurcan be reduced and the behavior of the automobile 1 can be stabilized.

Furthermore, as described with reference to step S28 in FIG. 6 , when,after the downshift point is set to the third gear-shifting point S3based on the coefficient of friction, the rotation speed of the inputshaft 8 a decreases to the third gear-shifting point S3, the controller20 interrupts motive power transmission between the input shaft 8 a andthe output shaft 8 b instead of starting gear-shifting. Interrupting themotive power transmission results in a decrease in a torque acting onthe rear wheels 2R. Accordingly, destabilization of the behavior of theautomobile such as an occurrence of an oversteered state can besuppressed and, at the same time, engine stall due to a further decreasein the rotation speed of the engine 4 can be avoided.

In addition, as described with reference to step S23 in FIG. 6 , in thecourse of deceleration during an operation of the brake pedal 19, therotation speed of the motor 5 during a regeneration operation can bemaintained at a high level by setting the downshift point to therelatively high first gear-shifting point S1. Maintaining a highrotation speed of the motor 5 increases a regeneration amount and,eventually, improves fuel efficiency performance of the automobile 1.

On the other hand, in the course of deceleration during a non-operationof the brake pedal 19 (during a non-brake pedal operation), a change toan acceleration request may occur when the driver depresses theaccelerator pedal 18. In this case, when the rotation speed of the inputshaft 8 a of the automatic transmission 8 is maintained at a high leveldue to setting the downshift point relatively high, there is a risk thata sufficient drive force cannot be secured during the accelerationrequest by the driver.

In consideration thereof, as described with reference to step S24 inFIG. 6 , during a non-operation of the brake pedal 19, the controller 20sets the downshift point of the automatic transmission 8 to the secondgear-shifting point S2 which is lower than the first gear-shifting pointS1. Accordingly, since the rotation speed of the input shaft 8 a of theautomatic transmission 8 becomes relatively lower, a sufficient driveforce can be secured during the acceleration request by the driver.

In addition, as described with reference to steps S61 to S64 in FIG. 11which follow step S28 in FIG. 6 , when an unstable behavior of theautomobile 1 diverges even after interrupting the motive powertransmission between the input shaft 8 a and the output shaft 8 b, dueto operation of DSC or ABS, the behavior of the automobile 1 can beprevented from becoming uncontrollable.

In addition, the controller 20 according to the present embodimentdetermines an oversteered state of the automobile 1 by receiving signalsof the yaw rate sensor 54 which outputs a signal related to a behaviorof the automobile 1 and the steering angle sensor 53 which outputs asignal related to a steering operation by the driver.

Accordingly, the controller 20 determines an oversteered state based onsignals of the yaw rate sensor and the steering angle sensor 53. As aresult, the controller 20 can determine the behavior of the automobile 1in a speedy and accurate manner.

It should be understood that the embodiments herein are illustrative andnot restrictive, since the scope of the invention is defined by theappended claims rather than by the description preceding them, and allchanges that fall within metes and bounds of the claims, or equivalenceof such metes and bounds thereof, are therefore intended to be embracedby the claims.

DESCRIPTION OF REFERENCE CHARACTERS

1 Automobile (vehicle)

19 Brake pedal

110 Steering wheel

20 Controller

2F Front wheel

2R Rear wheel

3 Friction brake system

4 Engine

5 Motor

53 Steering angle sensor (second sensor)

54 Yaw rate sensor (first sensor)

8 Automatic transmission

8 a Input shaft

8 b Output shaft

9 High-voltage battery

1. A vehicle gear-shifting control apparatus, comprising: an enginewhich is mounted to a vehicle and which generates a travel drive forceof the vehicle; a motor which generates another travel drive force ofthe vehicle and which supplies a battery with regenerative energy duringdeceleration of the vehicle; a hydraulically controlled automatictransmission which has an input shaft connected to the engine and themotor and an output shaft connected to a rear wheel of the vehicle andwhich subjects an input rotation to gear-shifting at a transmission gearratio corresponding to a selected shift stage and outputs thegear-shifted input rotation; and a controller which executes, at leastduring deceleration of the vehicle, a regeneration control of impartinga regenerative braking torque to the rear wheel by causing the motor toperform a regeneration operation and a gear-shifting control of changingthe shift stage by outputting a gear-shifting signal in accordance witha rotation speed of the input shaft to the automatic transmission,wherein the controller starts the gear-shifting control, triggered bythe rotation speed of the input shaft decreasing to a predetermineddownshift point during a downshift of the shift stage, and duringdeceleration of the vehicle when it is determined that a coefficient offriction of a road surface on which the vehicle travels is lower than apredetermined threshold in the regeneration control, the controller setsthe downshift point lower than during deceleration of the vehicle whenit is determined that the coefficient of friction is equal to or higherthan the threshold.
 2. The vehicle gear-shifting control apparatusaccording to claim 1, wherein during acceleration of the vehicle when itis determined that the coefficient of friction is lower than thethreshold, the controller limits an upshift which causes the shift stageto be changed to a predetermined stage or higher.
 3. The vehiclegear-shifting control apparatus according to claim 1, wherein when thedownshift point is set low based on the coefficient of friction and,subsequently, the rotation speed of the input shaft decreases to thedownshift point, the controller interrupts motive power transmissionbetween the input shaft and the output shaft.
 4. The vehiclegear-shifting control apparatus according to claim 1, furthercomprising: a hydraulically controlled friction brake system whichdistributes a braking force to a front wheel and the rear wheel of thevehicle in order to realize braking in accordance with a brake pedaloperation by a driver, wherein during the regeneration control in a casewhere the coefficient of friction is determined to be higher than thethreshold, the controller sets the downshift point higher in a state ofdeceleration of the vehicle during the brake pedal operation than thestate of deceleration of the vehicle during a non-brake pedal operationunder a same condition of the coefficient of friction.
 5. The vehiclegear-shifting control apparatus according to claim 3, furthercomprising: a hydraulically controlled friction brake system whichdistributes a braking force to a front wheel and the rear wheel of thevehicle in order to realize braking in accordance with a brake pedaloperation by a driver, wherein when an unstable behavior of the vehiclediverges after interrupting the motive power transmission between theinput shaft and the output shaft, the controller causes the frictionbrake system to execute a control for stabilizing the behavior of thevehicle by imparting the braking force to the front wheel or the rearwheel.
 6. The vehicle gear-shifting control apparatus according to claim5, wherein the controller determines an oversteered state of the vehicleby receiving signals of a first sensor which outputs a signal related toa behavior of the vehicle and a second sensor which outputs a signalrelated to a steering operation by the driver, and the controllerdetermines that the vehicle is engaging in an unstable behavior when thevehicle is in the oversteered state.
 7. The vehicle gear-shiftingcontrol apparatus according to claim 6, wherein the controllerdetermines whether or not the vehicle is in the oversteered state basedon a deviation between an estimated yaw rate which can be calculatedfrom the vehicle speed and the steering angle, and an actual yaw ratebased on a signal from the first sensor.
 8. The vehicle gear-shiftingcontrol apparatus according to claim 7, wherein the controllerdetermines that the vehicle is in the oversteered state when thedeviation between the estimated yaw rate and the actual yaw rate isequal to or larger than a predetermined value.